perf probe: Fix short file name probe location reporting

After adding probes, perf-probe(1) reports the probes locations which include
filenames for certain cases.

But for short file names (whose length < 32), perf-probe didn't display the
name correctly. It actually skipped the first character.

Here's an example where 'icmp.c' was screwed:

   $ perf probe -n -a "icmp.c;sk=*"
   Add new events:
     probe:icmp_push_reply (on @cmp.c)
     probe:icmp_reply     (on @cmp.c)
     probe:icmp_reply_1   (on @cmp.c)
     probe:icmp_send      (on @cmp.c)
     probe:icmp_send_1    (on @cmp.c)
     probe:icmp_error     (on @cmp.c)
     probe:icmp_error_1   (on @cmp.c)
     probe:icmp_error_2   (on @cmp.c)
     probe:icmp_error_3   (on @cmp.c)

This patch fixes this bug in synthesize_perf_probe_point().

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
LKML-Reference: <m31v588r9k.fsf@gmail.com>
Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>